1. Field of the Invention
The present invention relates to a method and an apparatus for processing an object to be processed, such as a semiconductor wafer.
2. Description of the Related Art
A semiconductor device fabricating method, in general, includes a film forming process for forming a thin film, such as a polysilicon film or a silicon oxide film, on an object to be processed, such as a semiconductor wafer (hereinafter, referred to as “wafer”) by, for example, CVD (chemical vapor deposition) or the like.
Generally, such a film forming process is carried out in a clean room to prevent the adhesion of contaminants to the wafer. It is difficult to clear the clean room completely of contaminants and the atmosphere of the clean room contains a very small quantity of organic substances (contaminants), such as tributyl phosphate (TBP), a siloxane and dioctyl phthalate (DOP). Consequently, in some cases, those organic contaminants adhere to the wafer. Formation of the thin film on the wafer thus contaminated with organic substances can deteriorate the characteristics of semiconductor devices and will reduce the yield of semiconductor devices. Therefore, the wafer is cleared of organic substances adhering thereto before forming the thin film on the wafer.
A cleaning method of cleaning a wafer is carried out by using, for example, a processing vessel 51 as shown in FIG. 9. A wafer 53 is mounted on a wafer support table 52 loaded into the processing vessel 51. Then, the wafer 53 is heated at a predetermined temperature of, for example, 600° C. by a heater 54 built in the wafer support table 52. Subsequently, a processing gas, such as oxygen gas, is supplied through a supply port 55 into the processing vessel 51. The oxygen gas supplied into the processing vessel 51 undergoes thermal decomposition in the vicinity of the wafer 53 and oxygen atom radicals (O*) are produced. The oxygen atom radicals decompose the organic substances adhering to the surface of the wafer 53. The thus decomposed organic substances are discharged from the processing vessel 51 through a discharge port 56. Thus, the wafer 53 is cleaned.
The allowable range of the quantity of organic substances adhering to the wafer 53 has been narrowed as the dimensions of device patterns shrinks to meet the increase of the number of components per semiconductor device. Thus, further efficient removal of organic substances from wafers is desired.
The aforementioned cleaning method needs to heat the interior of the processing vessel 51 (the wafer 53) at a high temperature of, for example, 600° C., to produce oxygen atom radicals, which is undesirable from the point of view of preventing the thermal oxidation of the wafer.
The aforementioned cleaning method takes much time for cleaning many wafers 53 because the aforementioned cleaning method cleans wafers 53 one at a time.
Moreover, it is possible that new organic substances adhere to a wafer 53 cleaned by the aforementioned cleaning method while the wafer 53 is carried to a thin film forming apparatus to form a thin film on the wafer.